template<typename System, bool LocalTimeStepping, template< typename > typename CacheTagPrefix = std::type_identity_t, typename = tmpl::conditional_t< tt::is_a_v<tmpl::list, typename System::variables_tag>, typename System::variables_tag, tmpl::list<typename System::variables_tag>>>
struct UpdateU< System, LocalTimeStepping, CacheTagPrefix, typename >
Perform variable updates for one substep.